Structure for adjusting paper path gap using the roller moving according to the thickness of the paper

Abstract

An image forming apparatus comprising includes an image carrying member including a movable surface to include a toner image; a transfer roller to form a transfer nip between the transfer roller and the movable surface of the image carrying member, to move position in a direction in correspondence to a thickness of a print medium to intersect a direction of introduction of the print medium into the transfer nip, and to receive a transfer bias voltage to transfer the toner image from the movable surface of the image carrying member to the print medium; and a movement guide structure to guide the print medium toward the transfer nip, and to move in synchronization with the movement of the position of the transfer roller to change a gap between an end of the movement guide structure facing the image carrying member and the image carrying member.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 an image carrying member including a movable surface to include a toner image; 
 a transfer roller to form a transfer nip between the transfer roller and the movable surface of the image carrying member, to move position in a direction in correspondence to a thickness of a print medium to intersect a direction of introduction of the print medium into the transfer nip, and to receive a transfer bias voltage to transfer the toner image from the movable surface of the image carrying member to the print medium; and 
 a movement guide structure to guide the print medium toward the transfer nip, and to move in synchronization with the movement of the position of the transfer roller to change a gap between an end of the movement guide structure facing the image carrying member and the image carrying member. 
 
     
     
       2. The image forming apparatus of  claim 1 , wherein, as the thickness of the introduced print medium increases, the gap between the end of the movement guide structure and the image carrying member increases. 
     
     
       3. The image forming apparatus of  claim 2 , wherein a difference between a gap between the end of the movement guide structure and the image carrying member in which a print medium is not introduced into the transfer nip and a gap between the end of the movement guide structure and the image carrying member in which a print medium is introduced into the transfer nip is greater than the thickness of the introduced print medium. 
     
     
       4. The image forming apparatus of  claim 2 , further comprising a connecting link to transfer the positional movement of the transfer roller to the movement guide structure, the connecting link to rotate about a first rotation center apart from a rotation center of the transfer roller, and comprises a first arm to extend from the first rotation center and to be pressed by the transfer roller, and a second arm to extend from the first rotation center in a different direction from that of the first arm and to face the movement guide structure. 
     
     
       5. The image forming apparatus of  claim 4 , wherein a distance from a point where the first arm is pressed by the transfer roller to the first rotation center is less than a distance from a point where the second arm contacts the movement guide structure to the first rotation center. 
     
     
       6. The image forming apparatus of  claim 4 , wherein the movement guide structure to rotate about a second rotation center apart from the rotation center of the transfer roller, and
 comprises a third arm to extend from the second rotation center and to be pressed by the second arm, and a fourth arm to extend from the second rotation center in a different direction from that of the third arm and to face the movement guide structure. 
 
     
     
       7. The image forming apparatus of  claim 6 , wherein a distance from the end facing the image carrying member to the second rotational center in the fourth arm is greater than a distance from a point where the third arm is pressed by the second arm to the second rotational center. 
     
     
       8. The image forming apparatus of  claim 6 , wherein the movement guide structure comprises:
 an elastic member to provide an elastic force such that the fourth arm moves toward the image carrying member; and 
 a stopper to limit a rotation range of the movement guide structure. 
 
     
     
       9. The image forming apparatus of  claim 1 , wherein the movement guide structure comprises:
 a rotating body to rotate about a second rotation center apart from a rotation center of the transfer roller; and 
 a guide sheet having a thickness less than a thickness of the rotating body and protruding from the rotating body toward the image carrying member. 
 
     
     
       10. The image forming apparatus of  claim 9 , wherein the thickness of the guide sheet is about 0.05 mm to about 0.4 mm. 
     
     
       11. The image forming apparatus of  claim 10 , further comprising:
 a pair of conveying rollers upstream of a transfer path of the print medium to transfer the print medium between the image carrying member and the transfer roller; and 
 a guide structure between the conveying rollers and the transfer roller and facing a second surface opposite to a first surface of the print medium guided by the movement guide structure. 
 
     
     
       12. The image forming apparatus of  claim 11 , wherein a gap between the guide structure and the movement guide structure is gradually narrowed along the transfer path of the print medium. 
     
     
       13. The image forming apparatus of  claim 12 , wherein a distance between an end of the guide structure and the image carrying member is 2 mm to 10 mm.